Integrated circuit devices have become essential components in a wide variety of products ranging from computers and robotic devices to household appliances and automobile control systems. New applications continue to be found as integrated circuit devices become increasingly capable and fast while continuing to shrink in physical size and power consumption. As used herein, integrated circuit device refers broadly to a device having one or more integrated circuit chips performing at least one electrical and/or optical function, and includes both single-chip and multi-chip devices. In multi-chip devices, each integrated circuit chip is usually separately fabricated or “built up” from a substrate, and the resultant chips are bonded together or otherwise coupled into a common physical arrangement.
Advances in integrated circuit technology continue toward reducing the size of electrical circuits to smaller and smaller sizes, such that an entire local electrical circuit (e.g., a group of memory cells, a shift register, an adder, etc.) can be reduced to the order of hundreds of nanometers in linear dimension, and eventually even to tens of nanometers or less. At these physical scales and in view of ever-increasing clock rates, limitations arise in the data rates achievable between different parts of the integrated circuit device, with local electrical circuits having difficulty communicating with “distant” electrical circuits over electrical interconnection lines that may be only a few hundred or a few thousand microns long.
To address these issues, proposals have been made for optically interconnecting different electrical circuits in an integrated circuit device. For example, in the commonly assigned U.S. 2005/0078902A1, a photonic interconnect system is described that avoids high capacitance electric interconnects by using optical signals to communicate data between devices.
One issue that arises in the context of these and other electrooptical devices relates to the vertical transfer of optical signals between different integrated circuit layers. For example, in a multi-chip photonic interconnect system, it is often desirable to optically transfer information between a top-facing integrated circuit layer of a first chip and a bottom-facing integrated circuit layer of a second chip placed atop the first chip. The first chip may contain dense electrical circuits, for example, while the second chip may contain waveguides, optical couplers, etc. for transferring the information to “distant” components. In another example, it may be desirable to optically transfer information between two different integrated circuit layers of the same integrated circuit chip.
As device sizes continue to decrease, one issue arises when multiple adjacent optical signals require coupling between a first integrated circuit layer and a second integrated circuit layer, the optical signals being emitted at closely spaced locations. For example, it may be desirable to closely space the emitting locations for correspondence with closely spaced local electrical circuits for which information is being optically transferred. Issues can also arise for the case of a single optical signal emitted from a single location on the first integrated layer, including horizontal signal leakage issues (which can increase ambient optical “noise” in the system) and/or coupling efficiency issues. Other issues arise as would be apparent to one skilled in the art upon reading the present disclosure.